The present invention relates to a process for preparing a polymer component that contain one or more degradants to facilitate degradation of the polymer component.
The use of plastics has given rise to improved methods of packaging goods. For example, polyethylene and polypropylene plastic films, bags, bottles, Styrofoam cups, blister packages, and the like provide stable, relatively unbreakable, chemically resistant light weight packaging. Conventional plastics used for packaging include, for example, polyethylene, polypropylene, polystyrene, polyethylene terphthalate, and polyvinyl chloride. Plastics have also found wide spread use in other disposable products such as, for example, disposable personal care products such as diapers, disposable work garments, and other disposable garments. The many advantages of plastics has lead to their increased usage in a variety of products. This increased usage, however, has created a serious environmental problem, since the plastic must be disposed of after it is used. As a result of the stability and durability of plastics, however, they tend to remain in our environment without decomposing after disposal. It has been estimated that over 50 percent of the annual tonnage of all manufactured synthetic polymers are applied as packaging materials and that 90 percent of this ends up as a component of urban garbage. It has also been estimated that recalcitrant plastic accumulates in our environment at a rate of 25 million tons per year.
Burning of plastics is an unsatisfactory disposal solution, since this tends to damage incinerators due to the large quantity of heat generated during combustion and the adverse effects from the discharged smoke that adds to air pollution and destruction of the ozone layer. Similarly plastics, unlike paper and cardboard, are not readily destroyed by natural means, such as degradation by micro-organisms, which degrade most other forms of organic matter and return such matter to the biological life cycle. Thus, burial in a waste site is also not an effective means of disposal. The resulting accumulation of plastics in our environment has tended to result in landfills becoming filled to capacity; unsightly litter destroying the scenery and landscape; and destruction of the living environment for marine life and other forms of life.
In an effort to resolve the environmental problem, additives have been combined in certain ways with the polymeric compositions used to make plastics to increase the rate at which the plastic is degraded to environmentally friendly compounds. These additives, commonly called degradants, increase the rate of degradation of the plastic by increasing the rate of photodegradation, biological degradation, and/or chemical degradation.
Photodegradation involves the natural tendency for most polymers to undergo gradual reaction with atmospheric oxygen, particularly in the presence of light. Typically, a photosensitizing agent is employed in order to accelerate this natural tendency. The photosensitizing additive absorbs ultraviolet light (e.g., from sunlight) and the additive, in the photo-excited state, then undergoes a chemical reaction that leads to the generation of free radicals, which leads to an auto-oxidation and eventual disintegration of the plastic. Photodegradation has generally involved two technological approaches: (a) introduction of photosensitive functional group into the polymer; or (b) adding of photosensitive reagents to the polymer. A copolymer of ethylene and carbon monoxide, such as those commercially available from Dow Chemical Co., DuPont Co., Union Carbide Co., and Bayer Co., or the vinyl ketone copolymer commercially available from Ecoplastics Co. are examples of introducing a photosensitive functional group into the polymer. The approach of adding photosensitive reagents is exemplified by the commercially available polymers of Ampacet Co. and Ideamasters Co. that contain an added metal complex, such as that developed by Scott-Gilead Co. as disclosed in U.S. Pat. No. 4,360,606. The thermal oxidation that follows the initial photochemical initiation step may be accelerated by the addition of auto-oxidizable substances. The auto-oxidizable substances may also increase the rate or efficiency of the photochemical step.
Biodegradable plastics developed so far include, as the degradable material, polymeric products of microorganisms such as poly-xcex2-hydroxybutylate, polymers synthesized from biochemicals produced by microorganisms, chemically synthesized aliphatic polyesters, or naturally synthesized polymers, such as starch or chitin.
U.S. Pat. No. 3,840,512 discloses thermoplastic compositions containing a metal salt of a fatty acid and a free carboxylic acid. Compression molded films which included both the metal salt of a fatty acid and a free carboxylic acid exhibited shorter times before the film became embrittled when exposed to light than films containing only the metal prodegradant.
U.S. Pat. No. 3,941,759 discloses a degradable plastic containing an organic photosensitizer and at least one organic derivative of a transition metal. Degradation is initiated by a photo-oxidative reaction of the photosensitizer and is sustained by the organic derivative of a transition metal. The plastic will continue to oxidize in the dark after an initial exposure to ultraviolet light.
U.S. Pat. No. 3,994,855 discloses thermoplastic polymers or copolymers of xcex1-olefins containing one or more transition metals. The polymer compositions are degraded under the action of sunlight and/or ultraviolet light and may also be subject to thermal degradation.
U.S. Pat. No. 4,101,720 discloses a degradable plastic composition that includes an organic polymeric material having dispersed therein at least one organic derivative of a transition metal and at least one readily autoxidizable organic material.
U.S. Pat. No. 4,156,666 discloses a degradable polyolefin resin comprising a polyolefin, a fatty acid or ester of a fatty acid and a monohydric aliphatic alcohol, and optionally an inorganic filler. The resins are molding resins and degrade when subjected to sunlight.
U.S. Pat. No. 4,256,851 discloses a degradable plastic composition comprising an organic polymeric material having dispersed therein at least one ethylenically unsaturated alcohol or ethylenically unsaturated ester derived therefrom as a readily autoxidizable substance.
U.S. Pat. No. 4,360,606 discloses a plastic composition containing an organic photosensitizer and at least one readily autoxidizable organic substance. Exposure of the polymeric material to an artificial source of light or sunlight initiates a chemical degradation process. The initial photochemical reaction is followed by susbequent reactions that are essentially thermal (i.e., non-photochemical). The readily autoxidizable substance accelerates the thermal autoxidation step that follows the initial photochemical step.
U.S. Pat. No. 4,461,853 discloses a controllably degradable vinyl polymer composition that contains a complex of two different metals. A combination of iron and nickel compounds provides enhanced photodegradation of the polymer composition.
U.S. Pat. No. 4,476,255 discloses a plastic composition containing a photosensitizer. Exposure of the plastic composition to natural sunlight or artificial sources of ultraviolet light initiates degradation of the composition.
U.S. Pat. No. 4,517,318 discloses a photodegradable styrene resin that comprises a styrene resin and at least one photodegradable agent selected from benzophenone, anthroquinone, fluorene, xanthone, phenylalkyl ketones, phenacyl halides, and derivatives of these compounds and optionally at least one photodegradable accelerator.
U.S. Pat. No. 4,931,488 discloses thermoplastic polymer compositions that include a biodegradable substance, such as starch; a transition metal compound; and a fatty acid or ester of a fatty acid. The compositions may further include one or more other transition metal compounds to catalyze degradation of the polymer. The polymer compositions are degraded under the action of heat and/or ultraviolet light.
U.S. Pat. No. 4,983,645 discloses that the addition of camphorquinone to polyethylene accelerates the photodegradation of the polymer when the polymer is exposed to ultraviolet light.
U.S. Pat. No. 5,091,262 discloses a biodegradable multilayer polyethylene film produced by a conventional extrusion process. The inner layer of the film contains about 3 to 40 percent starch and the exterior layers comprise polyethylene and at least one prodegradant to facilitate degradation of the outer layers and expose the starch filled inner layers.
U.S. Pat. No. 5,096,939 discloses a polymeric composition with enhanced reactivity toward oxidative and/or photo-oxidative degradation. The rate of degradation is enhanced by incorporating at least one alkoxylated ethylenically unsaturated compound as an organic photosensitizer. The compositions may further include other readily oxidizable substances.
U.S. Pat. No. 5,134,193 discloses a polyethylene copolymer modified to contain chromomorphic moieties, which absorb at wavelengths greater than 200 nm, such as para-substituted benzenes and anthracenes, chemically bonded thereto. The copolymer, when added to virgin polyethylene renders the composition more susceptible to ultraviolet radiation.
U.S. Pat. No. 5,145,779 discloses a process for degrading C2 to C8 alpha olefin starch containing polymers with lignin degrading microorganisms.
U.S. Pat. No. 5,258,422 discloses compostable and biodegradable thermoplastic compositions comprising a thermoplastic polymer, a hydrolytically unstable antioxidant, a pro-oxidant, an accelerator, and a property modifier.
U.S. Pat. No. 5,308,906 discloses an extrudable elastomeric composition composed of an elastomer A-B-Axe2x80x2 block copolymer, where A and Axe2x80x2 are each a thermoplastic polymer endblock and B is a conjugated diene monomer having a low degree of residual ethylenic unsaturation, a polyolefin, and an effective amount of transition metal compound distributed in the blend of the polyolefin and block copolymer. The elastomeric composition degrades in thermally oxidative environments.
U.S. Pat. No. 5,378,738 discloses a biodegradable plastic produced by adding a substance that imparts a hydrophilic property to the plastic so that the plastic is decomposed by Blasidomycetes.
U.S. Pat. No. 5,444,107 discloses a degradable polymer composition consisting essentially of a thermoplastic polymer composition comprising primarily polylactic acid or a copolymer of lactic acid and another hydroxy-carboxylic acid and starch and/or modified starch. The degradation rate of the polymer composition is controlled by the varying the amount of starch and/or modified starch.
U.S. Pat. No. 5,461,093 discloses a biodegradable polyethylene composition. The composition includes starch chemically bonding to polyethylene with a coupling agent, a radical initiator, a Lewis acid, an autooxidizing agent, and a plasticizer.
U.S. Pat. No. 5,565,503 discloses a film of a biodegradable polyolefin resin. The resin contains fillers selected from the group including inorganic carbonate, synthetic carbonates, nepheline syenite, magnesium hydroxide, aluminum trihydrate, diatamaceous earth, mica, natural or synthetic silicas, calcined clay, or mixtures thereof and a metal carboxylate as a prodegradant.
U.S. Pat. No. 5,854,304 discloses a chemically degradable/compostable additive package or concentrate that is added to polyolefins. The additive package is a combination of a metal carboxylate and an aliphatic poly hydroxy-carboxyl acid.
U.S. Pat. No. 5,861,461 discloses a biodegradable plastic composition characterized in that a thermoplastic modified starch is chemically bonded by the use of a coupling agent to a matrix resin of polyethylene and a biodegradable polyester.
U.S. Pat. No. 5,866,634 discloses a biodegradable polymer composition comprising polylactic acid mixed with a polyester type biodegradable polymer.
U.S. Pat. No. 5,973,024 discloses a biodegradable plastic composition and a method for controlling the rate of biodegradation of the biodegradable plastic. The rate of degradation is controlled by adding a carbodiimide compound to the biodegradable plastic. The carbodiimide is mixed into the plastic by dissolving the plastic and carbodiimide in an organic solvent and then removing the organic solvent by distillation or by mixing the carbodiimide with the plastic by melt-kneading.
WO 88/09354 discloses a degradable polymer composition that is a blend of a normally stable chemically saturated polymer and a less stable chemically unsaturated polymer or copolymer, an anti-oxidant active over a limited period of time, and a latent pro-oxidant, such as an organic salt of a transition metal.
WO 92/11298 discloses a photodegradable thermoplastic composition that includes a first transition metal compound, a second transition metal compound, and an aromatic ketone. The second transition metal compound acts as a catalyst with the first transition metal compound to enhance degradation of the thermoplastic material. The aromatic ketone has a synergistic effect that increases photodegradation of the plastic.
WO 94/13735 discloses a degradable thermoplastic compositions. The compositions include a thermoplastic polymer component combined with a directly biodegradable component, an oxidizable component, transition metal additives, and an aromatic ketone. The polymeric material degrades in three stages. The first stage is biological removal of the directly biodegradable component which results in mass reduction and a highly porous material. The second stage is chemical and results in oxidative shortening of the long polymer chains to decrease their molecular weight and the third stage involves biological metabolism of the low molecular weight fragments.
The one or more degradants are often added to virgin polymer compositions by melting pellets or powder of the virgin polymer and adding the degradants to the melted polymer, mixing the degradants and polymer in an extruder to disperse the degradants within the polymer, and extruding the mixture into pellets or other useable form of the polymer. Typically the degradants are added in an amount of about 0.5 to 2 percent based on the weight of the polymer. The resulting extruded polymer containing the degradants is then used in latter manufacturing operations such as, extrusion, film blowing, or molding to produce a final article. The process of melting the polymer to add the degradants, however, is expensive. For example, the remelting step includes the high energy costs associated with providing sufficient heat to remelt the polymer and the manpower costs to perform the remelting step. Moreover, the process is detrimental to the quality of the final polymer blend itself, since each event of heating and melting a polymer adds to the heat history of the polymer and tends to result in some degradation of the polymer.
More often, the one or more degradants are added to virgin polymer by master batching. Master batching involves adding a package that includes the degradants in the form of a master batch to the virgin polymer. A master batch is a blend of the polymer containing high concentrations of the degradants. The master batch is prepared by the process described above except that higher concentrations of degradants are added to the virgin polymer. Typically a master batch contains between about 5 to 20 percent of the degradants by weight of the polymer and may contain as much as 30 percent of the degradants by weight of the polymer. Polymer compositions for final use, having the desired lower concentration of degradants, are then prepared by combining remelted virgin polymer and remelted polymer from the master batch in a ratio so as to provide a desired final concentration. Typically the weight ratio of virgin polymer to master batch is about 5:1. An extruder, such as a twin screw extruder, is typically used to mix the two polymer compositions and to disperse the master batch degradants throughout the virgin polymer. The resultant mixture is then extruded into pellets or other useable form of the polymer for use in latter manufacturing operations such as, extrusion, film blowing, or molding to produce a final article.
The process used to make the master batch, however, involves melting the polymer to add the degradants and, thus, includes all the disadvantages discussed above that are associated with remelting a polymer to add a degradant. Moreover, combining a master batch with a virgin polymer has numerous other disadvantages. For example, it is difficult to homogeneously distribute the degradant throughout the final polymer mix, since it is difficult to thoroughly mix two polymer melts. Furthermore, master batches are inconvenient to use since, due to the high concentrations of degradants, they are susceptible to decomposition and therefore can only be stored for a limited length of time. Thus, they must often be ordered and shipped immediately prior to use. Furthermore, the high concentrations of degradants present in the master batch typically leads to deterioration of the polymer in the master batch and, thus, results in a final polymer that is of inferior quality. This is especially true when the polymer is subjected to the high temperatures necessary for extrusion or film blowing.
The difficulty in obtaining a polymer of high quality and the high costs associated with preparing polymers containing degradants has been a barrier to these products becoming commercially available. Thus, there is a need for improved methods of preparing polymer compositions containing degradants that are more cost effective and that produce a higher quality product. The current invention provides such a process.
The present invention is directed to a method for manufacturing a polymer component containing a degradant component. The method includes the steps of polymerizing one or more monomers to provide a fluid polymer component, and directly combining the fluid polymer component and degradant component to form a blend and to distribute the degradant component substantially homogeneously throughout the fluid polymer component. The method may further include the step of solidifying the blend sufficiently to inhibit further distribution of the degradant component in the blend. The combining may be accomplished with an extruder.
The degradant component may be added in an amount of about 0.01 to 10 percent by weight of the polymer composition, preferably in an amount of about 0.1 to 5 percent by weight of the polymer composition, and more preferably in an amount of about 0.5 to 2 percent by weight of the polymer composition. The degradant component may be one or more of a photodegradant, a biodegradant, or a chemical degradant. The photodegradant may be one or more of aliphatic or aromatic ketones, quinones, peroxides, hydroperoxides, azo compounds, organic dyes, latent sensitizers, aromatic hydrocarbons, or mixtures thereof. The biodegradant may be one or more of chitin, starch, cellulose, glucose derivatives, polysaccharides, poly-xcex2-hydroxybutylate, poly caprolactone, polyesters, carbodiimides, or mixtures thereof. The chemical degradant may be one or more of a combination of a metal carboxylate and an aliphatic poly hydroxy-carboxyl acid, a combination of metal carboxylate and filler, or a transition metal complex. The photodegradant may be further combined with one or more of an auto-oxidizable substance selected from the group consisting of olefinic materials, ethers, acetals, ketals, amines, aldehydes, natural oils, unsaturated fatty acids, natural and synthetic resins, and mixtures thereof. Preferably, the degradant component and fluid polymer component are homogeneously distributed. The degradant component may be a liquid.
The polymer component may be at least one of (i) homo- and copolymers of monoolefins and diolefins; (ii) copolymers of one or more monoolefins and/or diolefins with carbon monoxide and/or with other vinyl monomers; (iii) hydrocarbon resins including hydrogenated modifications thereof; (iv) homo- and copolymers of styrenes; (v) copolymers of one or more styrenes with other vinyl monomers; (vi) graft copolymers of styrenes on polybutadienes, polybutadiene/styrene copolymers, and polybutadiene/acrylonitrile copolymers; styrene or xcex1-methylstyrene and acrylonitrile or methacrylonitrile on polybutadiene; styrene and maleic anhydride on polybutadiene; styrene, acrylonitrile and maleic anhydride or maleimide on polybutadiene; styrene and acrylonitrile on ethylene/propylene/diene copolymers; styrene and acrylonitrile on polyalkyl acrylates or methacrylates; and styrene and acrylonitrile on acrylate/butadiene copolymers; (vii) halogen-containing polymers; (viii) homo- and copolymers derived from xcex1,xcex2-unsaturated acids and derivatives thereof; (ix) copolymers of homo- and copolymers derived from xcex1,xcex2-unsaturated acids and derivatives thereof with other unsaturated monomers; (x) homo- and copolymers derived from unsaturated alcohols and amines or the acyl derivatives or acetals thereof, and copolymers of these monomers with other ethylenically unsaturated monomers; (xi) homo- and copolymers of cyclic ethers and copolymers of these with bisglycidyl ethers; (xii) polyacetals; polyoxymethylenes which contain ethylene oxide as a comonomer; and polyoxymethylenes modified with thermoplastic polyurethanes, acrylates and/or MBS; (xiii) polyphenylene oxides and sulfides; (xiv) polyurethanes derived from hydroxy-functional components with aliphatic and/or aromatic isocyanates; (xv) polyamides and copolyamides derived from diamines, dicarboxylic acids, and/or aminocarboxylic acids or the corresponding lactams, with or without an elastomer as a modifier; block copolymers of polyamides with polyolefins, olefin copolymers, ionomers, chemically bonded or grafted elastomers, or polyethers; and polyamides condensed during processing (RIM polyamide systems); (xvi) polyureas, polyimides, polyamide-imides, polyetherimides, polyesterimides, polyhydantoins, and polybenzimidazoles; (xvii) polyesters derived from dicarboxylic acids, diols, and/or hydroxycarboxylic acids or the corresponding lactones; block copolyether esters derived from hydroxyl-terminated ethers; PETG; PEN; PTT; and polyesters modified with polycarbonate or MBS; (xviii) polycarbonates and polyester carbonates; (xix) polysulfones, polyether sulfones, and polyether ketones; (xx) crosslinked polymers derived from aldehyde condensation resins; (xxi) drying and non-drying alkyd resins; (xxii) unsaturated polyester resins derived from copolyesters of saturated and unsaturated dicarboxylic acids with polyhydric alcohols and vinyl compounds as crosslinking agents and halogen-containing modifications thereof; (xxiii) crosslinkable acrylic resins derived from substituted acrylates; (xiv) alkyd resins, polyester resins, and acrylate resins crosslinked with melamine resins, urea resins, isocyanates, isocyanurates, carbamates, or epoxy resins; (xxv) crosslinked epoxy resins derived from aliphatic, cycloaliphatic, heterocyclic, and/or aromatic glycidyl compounds which are crosslinked with hardeners; (xxvi) polysiloxanes; (xxvii) Michael addition polymers of amines or blocked amines with activated unsaturated and/or methylene compounds; (xxviii) polyketimines in combination with unsaturated acrylic polyacetoacetate resins or unsaturated acrylic resins; (xxix) radiation curable compositions containing ethylenically unsaturated monomers or oligomers and a polyunsaturated aliphatic oligomer; and (xxx) epoxymelamine resins such as light-stable epoxy resins cross-linked by an epoxy functional coetherified high solids melamine resin. In one embodiment the monomers comprise at least one of ethylene, propylene, styrene, or mixtures thereof. Preferably, the polymer component is substantially free of an inhibitor component.
The method may further include combining an inhibitor component with the fluid polymer in an amount sufficient to inhibit degradation of the polymer during processing. The inhibitor component may be added in an amount of between about 0.05 to 5 percent by weight of the polymer. The inhibitor component may also be added to the fluid polymer in an amount sufficient to inhibit degradation of the polymer during processing and for a specified amount of time after processing so that the polymer begins to degrade after the inhibitor component is depleted, wherein the specified amount of time after processing is the effective working life of the polymer. The inhibitor component may be an anti-oxidant. A nonreactive additive may also be added to the fluid polymer. The non-reactive additive may be processing aid, viscosity depressant, mold-release agent, anti-blocking agent, emulsifier, slip agent, anti-static agent, fibrous reinforcement additive, filler, flame retardant, lubricant, plasticizer, adhesion promoter, dye, pigment, or mixture thereof.
The present invention is also directed at articles that include a polymer component prepared according to the method of the invention. The article may be a molded article, extruded article, film, tape, or fiber.
The invention is also directed at methods of making a polymer article containing a degradant component. The method includes the steps of polymerizing one or more monomers to provide a fluid polymer component, directly combining the fluid polymer and degradant component to form a blend and to distribute the degradant component substantially homogeneously throughout the fluid polymer component, solidifying the blend of the fluid polymer component and degradant component, and forming the solidified blend into a polymeric article. The forming may involve the steps of remelting the solidified blend and shaping the blend into an article. The shaping may be accomplished by one or more of extrusion, extrusion blowing, film casting, film blowing, calendering, injection molding, blow molding, compression molding, thermoforming, or rotational casting.